US2010/0242863A1 describes a heat exchanger comprising walls out of aluminum. The walls enclose at least one water carrying channel and have at least one flue gas draft. At least one wall forms a boundary between the water carrying channel and the flue gas draft. The at least one wall is provided with fins and/or pins which enlarge the heat-exchanging surface and which extend in the flue gas draft. The heat exchanger has at least one water carrying channel comprising a number of consecutive parallel straight segments separated by U-turns. The heat exchanger comprises a combustion chamber for installation of a burner to generate flue gas.
EP16696892A2 discloses a heat exchanger that has a water carrying channel comprising a number of consecutive parallel straight segments separated by U-turns. The U-turns comprise deviating elements positioned in the water flow channel to deviate the water flow. The deviating elements extend over the whole length of a segment of a U-turn and correspond with the contour of the wall of the U-turn. The deviating elements are said to provide a more uniform water flow and a reduction of the pressure drop in the water channel.
GB1425473A discloses a sectional heat exchanger, particularly for use in gas or oil fired water heaters, made up of a plurality of side-by-side heat exchange units each comprising a pair of header sections interconnected by one or more finned tubes. Each header section is formed with an internal tapered socket at one end and an externally tapered surface at the opposite end, the ends of adjacent header sections being aligned and interfittingly received one within the other to define common supply and discharge headers. Each tube is in the form of a U-tube having straight portions connected by a return bend.